Method of making a saw chain



Jan. 28, 1964 A. V. BERNSTEIN ETAL METHOD OF MAKING A SAW CHAIN FiledJuly 27, 1960 INVENTORS Vilhelm Bernstein Andreas Buckmun United StatesPatent ()fifice Patented Jan. 28, 1964 3,119,234 METHOD OF MAKEIJG A SAWCHAIN Axel Vilhelrn Eernstein and Giof Andreas Baekman, both ofSandviken, Sweden Filed duly 27, 1960, Ser. No. 45,763 Claims priority,application Sweden June 22, 1959 1 Claim. (til. 76-112) This inventionrelates to saw chains of the type used on motor-driven chain saws, andmore particularly to links for saw chains and to the manufacturethereof. This application is a continuation in part of my copendingapplication Serial No. 37,888 filed June 22, 1960.

An object of this invention is to provide improved saw chains of thetype used on portable motor driven chain saws. A further object is toprovide improved cutter links for such saw chains. A still furtherobject is to reduce the effects upon saw chains of normal and abnormaluse and abuse. A further object is to overcome certain difficu'ltieswhich have been encountered with chain saws and to reduce to a minimumthe need for attention and service during use. These and other objectswill be in part obvious, and in part pointed out below.

In the drawings:

FIGURE 1 is a fragmentary view of a portion of a chain saw with partsbroken away; and,

FIGURE 2 is a view of a cutter of FIGURE 1.

Referring to FIGURE 1 of the drawing, the illustrative embodimentcomprises a chain saw having a saw chain 2 which is driven along theperipheral guide edges of a guide bar or plate 19, for example, to 'cutthrough a log or tree. Saw chain 2 is formed by an assembly of: cutterlinks 11; drive and guide links 3; connecting links 4; and, rivets 5which provide the interconnections between the links. The guide bar 19has peripheral grooves 8 and 9 into which the guide portions of thedrive and guide links 3 projects; and, the other links 11 and 4 restupon guide surfaces 6 at the sides of the groove. Referring to FIGURE 2,each of the cutter links 11 is formed by a central plate portion 12, anintegral depth gauge portion 22 and an integral cut-ting tooth 21. Thecutting tooth portion 21 comprises a shank portion 14 projecting awayfrom the central plane of the saw chain and a toe portion 15 whichprojects from the shank portion back to the central plane. The toeportion may be an acute angle or a right angle to the central plane. Thesaw chain includes cutter links of right and left configurations, and italso may include other types of cutting or slicing tooth links.

In the past, it has been standard practice to form the links of sawchains from carbon or low alloy steels. Saw chains formed of such steelshave inherent disadvantages. For example, during use, the chain movesvery rapidly along the guide bar, and the cutting links engage the woodso as to subject the links to substantial forces in the forms of steadypressures against the surfaces 6 and impact actions. This producesfriction between the various portions of the chain links and thesupporting and guiding surface. Chain saws are used under very severeand extreme weather conditions, and it is diflicult to insure that thechains are properly serviced and lubricated. For example, during thewinter months in northern climates when the ambient temperature is verylow, a chain saw may be operated for long periods of time when theoperator is unaware of the need for service and lubrication. During aperiod when a chain saw is not properly serviced or lubricated, theprior chains have been heated up by the high friction to temperatureswhich are above the transformation temperatures of the steels. Suchactions have, in effect, heat-treated portions of the links so as tomake them brittle and fragile, with the result that the link of the sawchain chains failed. This action may be referred to as frictionhardening of the links or link portions. It causes extreme hardness andbrittleness, with the result that fissures appear at the edges of thelinks, and the links break.

In accordance with the present invent-ion, saw chains or links, or partsor portions thereof, are formed of high chromium steel withcharacteristics rendering the chain relatively free from difiiculties ofthe nature discussed above. The high chromium steel, of which theselinks are formed, is transformed to austenite at a relatively hightemperature, and when it cools, it forms martensite, and it is thentempered. During the use of the saw chain, the high temperatures areproduced for very short periods of time at any particular portion of alink, and it has been found that links formed of this steel Willwithstand such temperature conditions very well. That is, the steel isnot hardened under the conditions of use which harden low-alloy steels.

In the illustrative embodiment, the saw chain links are formed of amartensitic high chromium steel containing the following: chromiuml2% to16%; carbon-20% to 35%; silicon-preferably 10% to .35 and not more than.40%; n-ickel-not more than 30% and preferably not more than 20%;manganese-not more than 1%, and preferably not more than .5 and, ironwith normally appearing impurities. As a specific example, the cutterlinks 11 may be formed of steel containing: carbon--.25 to 30%,preferably 30%; silicon-15% to 35%, preferably 30%; manganese-.15 to 35%and preferably 30%; phosphorusnot more than 030%; sulfur-not more than030%; nickel--not more than 20%; chromium-13.5% to 14.5% and preferably14%; and, iron with normally appearing impurities. In forming a cutterlink 11 from this steel, the blank is stamped from cold rolled strip orsheet steel, and the cutting tooth portion 21 is then formed in dies tothe desired shape. Illustrativerly, the links are then hardened from atemperature of 1050" C. and, after that, they are tempered at 200 C. Thelinks are then sharpened to form the cutting edges; and, the chain isassembled utilizing the other links which have been similarly stampedfrom the same steel, and then hardened and tempered.

As another example, with a chromium content of the order of 16%, thesteel may contain: 30% carbon; 35% silicon; 15% nickel. Generally thesteel contains at least 12% chromium, but not more than 16% chromium.Generally the carbon content must be at least 20%, but not more than35%. The manganese content of the steel does not appear to influence thequalities of the steel which are pertinent to the purposes of thepresent invention, except that the manganese content should not be morethan 2%, and preferably not more than 1%. The steel for the cutter linksshould not contain excessive amounts of certain other elements, such as:titanium, niobium, tungsten and vanadium, because those elements tend tointerfere with the ductility during forming of the cutter links.Illustratively, the steel may contain the following elements up to thepercentages indicated, but with a total for all of them of not more than2% vanadium- .5 molybdenum1.0%; titanium-1.0%; boron- .l%; andaluminum.1%. Also, the total quantity of titanium, niobium and tantalumshould not exceed 1%, and the total of molybdenum and tungsten shouldnot be more than 1%. Also, cobalt should not be more than .4%. While ithas been indicated that the chromium content may be between 12% and 16%, it is commonly between 13.5% and 14.5%, and, illustrativelly, is14%.

As indicated above, chain 2 is formed with at least links 11 made of thesteel indicated above. The links 3, 4 and 5 may also be made of anidentical steel. However, rivets 5 are of carbon or low al-loy steel.

This invention contemplates that links 11 may have different portionsformed of different steels, so as to give each portion the optimumcharacteristics. For example, cutter links 11 may have the cuttingteeth, or merely the toe portions, formed of one specific steel, whilethe central plate portion 12 is formed of another steel. The steels fromwhich the links are formed in accordance with the present invention havebeen referred to as martensitic high-chromium steel, which are steelshaving a chromium content of the order of 12% to 16%, and which havebeen heat treated and cooled toproduce a martensitic structure in thesteel which structure is very hard. This martensitic steel is thentempered to give it an improved ductility. While this class of steelshas been referred to as high-chromium steel, it should be noted thatthese steels are also identified as stainless steels. Hence, the linksand the saw chains formed therefrom have the added advantage of beingresistant to rust and corrosion.

The friction hardening effect referred to above is very serious with theside links 4 which move along the surface 6. Cutter links produced inaccordance with the present invention have improved edge wearcharacteristics. That is, they remain sharp for a long period of time.Links produced in accordance with the present invention haveconsiderably increased ductility or toughness, and resistance to shock.Impact tests have shown that links of this type are very resistant tothe damage of impact. The fatigue strength is also improved.

The illustrative embodiments of the invention are found to be verysatisfactory from a standpoint of forming the cutter links when thesteel is in the annealed condition.

The method of forming the links may be outlined as follows:

(1) Anneal the bands, strips or sheets of cold rolled steel, or thestamped-out links, at a temperature between 750 and 850 C., preferablybetween 800 and 825 C. Cool very slowly from the hardening temperaturedown to at least 500 C. or 600 C. From 500 C. or 600 C., the cooling maybe more rapid, for example, by exposure to air.

(2) Bend the cutting teeth in a die, or in another manher.

(3) Harden the links from a temperature between 950 C. and 1100 C., andpreferably from 1050 C. By this hardening, the previous ferriticstructure becomes martensitic.

(4) Temper at a temperature between C. and 425 C., preferably between C.and 300 C., and illustratively, 200 C. The tempered links should be ashard as possible without adversely affecting the ductility or toughness.Illustratively, the hardness should cxceed SOH (Rockwell C) and commonlymay be as high as 52 to 54H (Rockwell C).

(5) Sharpen the cutter teeth 11.

(6) Assemble the links and rivets into a saw chain.

As many possible embodiments of this invention may be made, all withoutdeparting from the scope of the invention, it is to be understoodthat,all matter hereinabove set forth, or shown in the accompanyingdrawings, is to be interpreted as illustrative and not in a limitingsense.

What is claimed is:

The method of forming a saw chain of the type which includes linkshaving integral cutting teeth, the steps of: stamping a link blank for alink which has an integral cutting tooth from a strip or sheet of coldrolled steel which is formed of iron and the normally appearingimpurities and which contains, 12% to 16% chromium, 20% to 35% carbon,not more than 35% silicon, and not more than 35% nickel; forming thelink from said link blank; hardening the link from a temperature between950 C. and 1100 C. to form martensitic steel; tempering the link at atemperature between 150 C. and 425 C. to a hardness of at least 50Rockwell C; sharpening the cutting tooth; and assembling .the link thusformed with other links to produce a saw chain.

References Cited in the file of this patent UNITED STATES PATENTSSteels, published by the American Society for Metals (Cleveland, Ohio),1935, pages 228 and 229 relied upon,

